The invention relates to a shaft with a co-rotating element fitted and secured to it, the shaft being cylindrical at least in the region in which the element is fitted, and the element having a cylindrical seating surface and at least one surface which is located perpendicular to the seating surface, and the welding taking place in the fillet formed between the seating surface of the shaft and that surface of the element which is located perpendicular to the seating surface. The term region is to be understood as meaning the location where the element is secured and the area surrounding it in at least one longitudinal direction.
The shaft may be a drive shaft, transmission shaft, crankshaft, camshaft or balancing shaft of a piston engine, and the co-rotating element may therefore be any desired flange, a wheel or gear, part of a clutch, a cam or a balancing weight. Consideration may be given in particular to shafts which run at high rotational speeds and are therefore subject to high demands in terms of accuracy and true running. Shafts of this type generally consist of a heat-treated steel or a case-hardened steel, while the elements often consist of a carburizing steel or a case-hardened steel and/or are forgings, investment castings or sintered parts.
Materials which are advantageous and preferred for the co-rotating part are steels with a carbon content of less than 0.45% or cast iron or nodular cast iron, with at least 40% of the matrix of the basic microstructure being formed by ferrite, remainder pearlite, martensite or bainite.
With parts of this type it was hitherto held to be an immutable law that a direct welded joint—in particular by arc welding—has to be avoided, apart from special solutions using friction welding or laser welding. There are two reasons for this: firstly, heating of the shaft causes it to be distorted, which has an adverse effect on true running; secondly, cracks are formed at the start and/or end of the welding bead, reducing the long-term strength and/or leading to premature fractures. The formation of the cracks can be explained, inter alia, by the fact that the establishing and collapsing of the arc cannot be synchronized with the melting of the welds.
It is an object of the invention to make parts of this type accessible to direct welding, in particular arc welding. The shaft and element are to be welded in such a way that a long-term joint is formed without the accuracy, true running or long-term strength being impaired.